We examined the use of DFA-Detrended fluctuation analysis-of heart rate variability during general anesthesia in order to assess the depth of anesthesia.

In this study, we observed changes in α₁, the short range scaling exponent, in α₂, the long range scaling exponent, and in the α₂/α₁ ratio during enflurane anesthesia. We monitored 7 stages during general anesthesia, i.e., 1) preoperation (awake state), 2) during induction, 3) after induction, 4) during maintenance, 5) before extubation, 6) after extubation, and 7) postoperation (Next day).

The α₂/α₁ ratio increased during the induction and extubation state compared to preoperation (awake state). This may be related to increased sympathetic activity due to stimulation of the autonomic nervous system. In the postoperation (awakened state), the ratio returned to the preoperation value (awake state). These results are similar to low frequency (LF), high frequency (HF) and LF/HF ratio values which reflect activity of autonomic nervous system.

Detrended fluctuation analysis parameters, especially the α₂/α₁ ratio, would be used for monitoring the depth of anesthesia. Also these parameters are useful indexes with the LF/HF ratio for the evaluation of sympathetic activity during general anesthesia.